#define  _CRT_SECURE_NO_WARNINGS  1
#include <stdio.h>
int fun(int a, int b)
{
	long  x = 1, y = 1;
	if (0 == b)
		return 1;
	while (b)
	{
		x = x * a;
		a--;
		y = y * b;
		b--;
	}
	return x / y;
}
int main()
{
	int n = 0;
	scanf("%d", &n);
	int a = n, b = 0, count = 0;
	int i = 0;
	while (1)
	{
		count = count + fun(a, b);
		a--;
		b++;
		if (2 * i >= n)
			break;
		i++;
	}
	printf("%d", count);

	return 0;
}